This invention relates to the expansion of tubes or sleeves within tubes. It has particular relationship to, and is uniquely suitable for the measurement of the expansion of the tubes or sleeves in tubes of the steam generator of a nuclear-reactor plant which conduct the coolant, i.e., of the primary tubes or their sleeves. The tubes extend into the region of the generator where the feedwater is injected and the heat energy derived from them converts the feedwater into steam. Transverse baffles through which the tubes extend position the tubes. It has been found that the feedwater and steam which flows around the tubes causes them to vibrate. To suppress or reduce substantially the vibration it is desirable to expand the tubes where they pass through the baffles. Typically the expansion should be such that the outer diameter of a tube is 0.001 to 0.003 smaller than the diameter of the hole in the baffle through which it passes.
Another occasion for tube expansion arises in the case of a sleeve which is inserted in a primary tube that has become corroded. In this case, it is necessary to expand the inner end of the sleeve so that it is in engagement with the corroded tube around its periphery. An effective brazed joint may then be produced between the inner end of the sleeve and the sleeved tube. Instead of being brazed the sleeve may be rolled into the tube. The rolling secures the sleeve firmly in the tube and essentially seals the sleeve to the tube.
Typically the expansion takes place during the sleeving. The sleeve inserting tool has an expansion mandrel which penetrates through the sleeve blank. When the sleeve blank is fully inserted in a tube, pressure is applied through the expansion mandrel to expand the sleeve near to inner rim. The pressure applied expands both the sleeve and the part of the tube backing up the sleeve. The sleeve is thus locked in position and does not roll out when the sleeve insertion member is removed.
It may also be desirable to expand the portion of the tube within the tube sheet which separates the secondary region of the generator from the inlet and outlet plenums of the generator although such measurement is not customarily necessary.
It is necessary to preclude expansion of the primary tubes or sleeves so that they are ruptured or are reduced in thickness. Because of the reduced thickness the sleeves or tubes may be ruptured by the coolant flowing through them or the fluid around them. In particular expansion of the sleeves near their upper rims must be limited because the sleeve is backed up only by the tube in this region and may be blown out of the expansion is unlimited. To accomplish the object of limiting the expansion, it is essential that the expansion of the tubes or sleeves be measured while they are being expanded. The expansion, monitored in this way, can be stopped when the thickness of a tube or sleeve has been reduced to a safe but useful magnitude. The interior of the steam generator is highly radioactive and it is necessary that the expansion be measured out of the radioactive environment of the generator. It is an object of this invention to measure the expansion of the primary tubes of a steam generator or of sleeves within the tubes without exposure to radioactivity, while the tubes or sleeves are being expanded. More generally, it is an object of this invention to measure the expansion of a tube while it is being expanded.